TRIAC simulation is not working right

#include <16F877A.h>

#FUSES NOWDT                    //No Watch Dog Timer
#FUSES NOBROWNOUT               //No brownout reset
#FUSES NOLVP                    //No low voltage prgming, B3(PIC16) or B5(PIC18) used for I/O

#use delay(crystal=20000000)

int increment_scr = 0;

#int_EXT // Zero Crossing Interrupt
void EXT_isr(void)
{
    output_low(PIN_B2);
    delay_ms(increment_scr);
    output_high(PIN_B2);
    delay_ms(1);
    output_low(PIN_B2);
    //delay_ms(increment_scr);
}


void main()
{
    set_tris_b(0b0000001);  // setting the I/O pins of port B --> 1 pin will be set as input --- 0 as digital output
    
    enable_interrupts(INT_EXT);   // enabling external interrupt
    ext_int_edge(H_TO_L);         // external interrupt raise when signal goes from high to low
    enable_interrupts(GLOBAL);    // all interrupt are enabled

   while(1)
   {
      if(input(PIN_D0) != 1) // If push Button pressed then increment the value.
      {
         while(input(PIN_D0) != 1){}
      
         if (increment_scr >=9) increment_scr = 9;
         else increment_scr++;
      }
      
      if(input(PIN_D1) != 1) // If push Button pressed then decrement the value.
      {
         while(input(PIN_D1) != 1){}
      
         if (increment_scr <=0) increment_scr = 0;
         else increment_scr--;
      }
   }
}